The present invention relates to a sensor and indicator for detecting a clogged condition of an ink filter disposed an ink supply conduit of an ink jet printing apparatus or the like.
Ink jet printers are becoming increasingly popular due to their high speed of operation and print quality. Such printers comprise an ink ejection head which is moved relative to a sheet of paper in the horizontal direction. Ink is supplied to the ink jet head under pressure through a small diameter conduit. During movement of the ink jet head across the paper, electrical pulses are fed to the ink jet head causing ejection of small drops of ink onto the paper. A pulse is fed to the ink jet head at each position at which it is required to print a dark spot or dot on the paper. After printing of one line of dots, the paper is moved relative to the ink jet head in the vertical direction and the ink jet head is again moved horizontally for printing the next line of dots. This operation is continued until an entire page has been printed. An ink jet printer is capable of printing not only alpha-numeric characters but also graphic designs under computer control.
In practical application it has been difficult to prevent clogging of the ink jet head with foreign matter and the like. The problem is compounded by the fact that the ink itself tends to coagulate in its container. For this reason, it is desirable to provide an ink filter in the ink supply conduit. Such an ink filter is capable of preventing a large amount of foreign matter and coagulated ink from reaching the ink jet head to clog the same. However, over a period of time the ink filter itself tends to become clogged.
Ink jet printers known heretofore have not had any means of determining the amount of clogging of the ink filter. Thus, it has been impossible to anticipate the time at which an ink feed failure or stoppage will occur due to excessive clogging of the filter. Since the rate at which the filter becomes clogged as a function of time and ambient operating conditions of the ink jet printer has not been known, it has been impossible to replace the filter after a suitable period of use in such manner that the filter will not become clogged from overuse nor will it be replaced prematurely while it still has a portion of its useful life remaining.
The disruptive effects of a printer failure during a busy business day due to an ink feed stoppage are well known to corporate and government office management personnel. Printer down time is increased due to the fact that it is not possible to determine immediately whether the ink feed stoppage is due to depletion of ink in the supply reservoir, clogging of the ink filter or clogging of the ink jet head. Where it is determined that sufficient ink remains in the reservoir, it has been necessary to disassemble the filter and/or ink jet head to determine the point of stoppage.